At the "Press Start" screen, press [Up] two times, [Down] two times, [Left], [Right], [Left], [Right], [Projectile], [Jump] two times to unlock all skins at the "Unlockables" menu. If you entered the code correctly, you will hear a sound.

Bonus skins

Successfully complete the indicated task to unlock the corresponding skin:

Axel Gear: Successfully complete Arcade mode on the Hard difficulty, using the secret damage move on every Boss.

Gold Sparkster: Successfully complete Gold Sparkster mode.

Secret damage moves

Damage the following Bosses with the indicated technique. If done correctly, you will hear a sound. Defeat the boss, and the next level will then be in Hard mode.

Axel Gear: Have him get hit by the tracking purple ball attack that he uses.

Wolf King: Wait for him to stand on top of a breakable floor block. Hit him until laughs, then drill attack the floor so he falls.

Wolf Robot: Reflect his dynamite back at his face.

Gold Sparkster mode

Successfully complete Arcade mode on the Hard difficulty, using the secret damage move on every Boss.

Steam achievements

Successfully complete the indicated task to unlock the corresponding achievement. To view your achievements and stats in Steam, select "Community", "My profile", "View all my games", then the game and view stats.

Bunker Buster: Complete world 3.

Burst Friends: Defeat 5 enemies in a single Rocket Burst or Drill attack.